The United Nations will observe Earth Hour on Saturday, by turning off the lights for one hour at its headquarters in New York and other facilities around the world, UN officials said here on Friday.

The world body will join scores of other landmarks around the globe that are participating in the Earth Hour event. In 2011, more than 5,200 cities and towns in 135 countries worldwide switched off their lights for Earth Hour to show support for action on climate change.

UN Secretary-general Ban Ki-moon said that the UN was turning off its lights "in solidarity with the men, women and children -- 20 percent of all humankind -- who live with no access to electricity."

Calling Earth Hour "a symbol of our commitment to sustainable energy for all," Ban said: "We need to fuel our future with clean, efficient and affordable energy."

"By acting together today, we can power a brighter tomorrow. The United Nations is strongly behind this cause from Earth Hour to Rio+20," the secretary-general said, referring to the UN Conference on Sustainable Development slated for June in Brazil.

Earth Hour, launched in 2007 in Australia by the World Wide Fund for Nature (WWF), which is a global conservation group, calls on people, organizations and cities to turn off their non- essential lights for one hour starting at 8:30 p.m. local time.

This is the third year that the United Nations joins hundreds of millions of people around the world in switching off the lights.

Sha Zukang, UN under-secretary-general for economic and social affairs and secretary-general of the Rio+20 conference, said Earth Hour is a significant and popular event that helps people think about the need to take actions that promote sustainable development.

"We cannot continue business as usual. We need to rethink the way we use our resources, how we promote well-being and protect the environment. We need to pursue new ideas," he said.

"The purpose of Rio+20 is to launch actions that will help us achieve sustainable development," Sha added.

The Earth Hour event takes place roughly one week after the vernal equinox -- when night and day are of the same duration in both hemispheres, ensuring that it will be dark everywhere in the world at 8:30 in the evening.